In recent years, various electronic components and devices, such as an illuminated key entry system, a defogger timer, a seat belt warning system, a light turning-off reminding warning system, a key takeout reminding warning system, power door locks, and a keyless entry system, have been independently installed and distributed in a vehicle. These electronic components are electrically connected with a meter unit mounted in front of the driver's seat. The electronic components are controlled by system means such as a microcomputer incorporated in the meter unit. The state of the vehicle detected by the electronic components is displayed on the meter unit if necessary for example, see Japanese Unexamined Patent Publication No. 203553/1995.)
Integration of the distributed, independent electronic components is considered as a means for achieving cost reduction. The combination of the required electronic components differs according to the vehicular specifications for specific climatic areas or the vehicle grade. Therefore, if electronic components are integrated simply according to the combination, then the number of variations increases. Consequently, large cost reduction cannot be expected.
Japanese Unexamined Patent Publication No. 276571/1994 discloses a multiplexed transmission device for a vehicular electric system. This multiplexed transmission device is separate from electronic components, unlike the prior art device. Since these two kinds of systems can be separately developed and manufactured, it is possible to prevent the total number of components including both electronic components and multiplexed transmission device from increasing. Even with this structure, however, the number of variations described above cannot be sufficiently decreased.
Accordingly, the present applicant has proposed novel means in Japanese Patent Application Nos. 60601/1997 and 69497/1997. In particular, electronic components other than the meter unit are classified and integrated into plural electronic component units. Mounting means are provided to mount and detach the electronic component units to and from the meter unit. A control portion for controlling the electronic component units and a power-supply portion for supplying electric power to the electronic component units are mounted in the meter unit. The electronic component units are controlled and energized via the mounting means. The present invention is an improvement over this proposed instrumentation system. It is an object of the present invention to improve the reliability of instrumentation devices.